1. Field of the Invention
The present invention relates to a light emitting display panel using an organic EL (electroluminescence) element as a self light emitting type element and a self light emitting type display module provided with drive means for driving to light this. More particularly, the present invention relates to a self light emitting type display module provided with a function capable of detecting a state in which a lighting fault is generated in mainly the self light emitting element of the light emitting display panel or a state having a high possibility that the lighting fault may occur in the future and a verification method for the fault in the same module.
2. Description of the Related Art
A number of electronic appliances and the like provided currently include a display and the display is indispensable as a man-machine interface for machines supporting the information society. The aforementioned display has been demanded to have a stricter reliability than displays adopted in such consumer machines as portable phone and car audio appliance if it is used in fields in which display faults can influence on human life like for example, medical equipment and airplane gauges.
In an injection appliance, for example, if brightness leak phenomenon occurs in the scanning line direction in a numeral display portion indicating an amount of injection, such a problem that a displayed numeral cannot be recognized to be “0” or “8” can occur. Further, a pixel at a portion displaying a decimal point is not lit so that a numeric digit is displayed erroneously and as a consequence, there may occurs a problem that the numeral may be read out mistakenly without this point being noticed. User's continuous use of the aforementioned machine mistakenly recognized that the display in such a fault condition is in normal condition is extremely dangerous and needless to say, this may lead to a fatal problem.
Thus, the display used in the electronic appliances is inspected for the fault condition of each of the pixels disposed on a display panel in a half completed condition prior to shipment of a product and whether or not the fault level satisfies the standard of a product on which the display is to be loaded is judged (see, for example, Japanese Patent No. 3437152).
The invention disclosed in the Japanese Patent No. 3437152 intends to execute the evaluation of each pixel of the display panel in the half completed condition prior to the shipment and aims at providing an evaluation device capable of obtaining a highly reliable evaluation result using a detection drive circuit of the organic EL display.
Although if the evaluation device disclosed in the Japanese Patent No. 3437152 is used, such an effect that an initial fault of a product can be found out and an appropriate measure can be taken before the display panel having the fault is delivered to user can be enjoyed, this kind of the display has a problem that a new fault can be generated in pixels disposed on the display panel during an operation of the display unit after the product is shipped.
Thus, various measures have been taken to minimize the extent in which such a fault occurs to secure reliability. However, to solve the fault in the pixel generated during the operation of the display and a problem that a fault may occur in the aforementioned drive means or the like, there exist extremely many technical problems and it is almost difficult to provide a display module in which no aforementioned fault occurs after the product is shipped.
On the other hand, as for the self light emitting element having a diode characteristic represented by the organic EL element, it has been well known that generally it has a very high impedance characteristic when reverse bias is applied thereto. However, the inventor of this application has reached a finding that by verifying the impedance characteristic of the element when the reverse bias is applied precisely, a state having a high possibility that a lighting fault may occur in the future can be detected (there exists a latent fault factor).